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Author Topic:   $20 Software Radio AIS Receiver
jharrell posted 12-31-2012 01:05 PM ET (US)   Profile for jharrell  
I have had an interest in radio for some time and as a software programmer have been very interested in getting into software defined radio: but the cost for the hardware has been to high for me to just experiment with.

Recently it was discovered that certain European standard DVB-T digital TV tuners can be put into a mode where the raw I/Q samples of 2 MHz wide are sent to the host and these tuners can are capable of 25 MHz to 1700 MHz reception! This effectively makes these devices $20 wide-band software defined receivers:

AIS is broadcast at 161.975 MHz and 162.025 MHz using narrow FM modulation, this is easily tunable by the RTLSDR devices, in fact both channels can be captured simultaneously as they fit well within 2 MHz. Along with software that can decode the digital information from the FM signal such as ShipPlotter you can plot any ship in range with $20 of hardware.

Here is a video of someone successfully doing so, using the same software I do:

This is only scratching the surface of these devices, so far I have successfully received local wide FM radios stations, NOAA Weather, local public safety trunked radio in 800 MHz, digital pagers in 900MHz, smart power meters, and the aviation equivalent of AIS called ADS-B to plot planes in flight along with aviation AM communication. All this with the little tiny whip that came with the device inside on my windowsill. A better antenna would do so much more, that is my next project. They use very small odd connectors (MCX) so adapters may need to made or purchased for more conventional BNC to use with other antennas.

I purchased mine through NooElec on Amazon: dp/B009U7WZCA/ref=?ie=UTF8&m=A2JO7YP9I9Y3D6 They also sell at up-converter to allow these device to receive below 25MHz.

I use the following software on a Windows PC: . This seems to be the most popular for theses devices and is interesting to me because it is written in the language I work with every day (C#) so I can read the code and understand how radio is demodulated from a programming perspective. I believe some been able to get it to work on a Mac using Mono, but otherwise I hear GQRX is a good one to use: osx-port-of-the-awesome-gqrx-sdr-software

Whats also interesting is there is a utility called RTLSDR TCP that can publish the radio samples over TCP/IP allowing you to have one lower power computer that has the receivers connected to it, perhaps closer to your antenna while doing demodulation somewhere else over the network say in your office with a faster computer. Some have used this in combination with a small cheap embedded computer such as a Raspberry Pi in an external enclosure to place the receiver up near their antenna outside.

I thought this would be interesting to post here because of the AIS aspect and from what I gathered jimh works with radio, but if you have any interest in radio and know a little about computers it is an cheap and fun way to get into the hobby.

jimh posted 12-31-2012 07:38 PM ET (US)     Profile for jimh  Send Email to jimh     
The notion of a software-defined radio (SDR) has been on my radar screen for a while, but I have not jumped into that realm. I guess I still have enough hardware radios sitting around to fiddle with this winter.

Yes, a good antenna will make an astonishing difference. For my house AIS receiving antenna I use a custom-designed three element yagi on a mast on the roof. I am occasionally getting ships down in Lake Erie (in the main beam of the antenna) that are over 50-miles away, and that is over a path of mostly urban terrain. I am quite amazed by that.

If you hang a decent antenna on the front end of our software-defined radio you will probably see much better results.

One of the problems for me with projects like this SDR is the experimental software is usually written for Windows-OS. I don't have a Windows-hardware machine. I do have a virtual Windows machine, but it is probably not going to work with a bleeding edge software project like the software-defined radios.

I browsed the support page for the MacOS port, and it looks like there are some problems getting it to run on the hardware and software that I have. I will probably have to take a pass on this for a while. But I think it is a very cool concept, and I look forward to hearing more results with your experiments.

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